Field
The present specification generally relates to molds for shaping glass-based material and, more specifically, molds having coatings for high temperature use in shaping glass-based material.
Technical Background
Glass articles can be formed into 3D shapes by heating the glass to a visco-elastic state and contacting the glass with a mold. However, forming three-dimensionally shaped glass articles with high softening point glass compositions, such as alkali aluminosilicate glass compositions, can be challenging. For example, some glass compositions have high softening points (sometimes greater than 900° C.), which makes a precision molding process more difficult since the glass needs to be heated to higher temperatures in order to reach a visco-elastic state suitable to forming. Additionally, some glass compositions have high percentages of sodium (such as, for example, greater than 10 mol %). Sodium may be highly mobile and reactive at high temperatures. Contacting a mold surface with sodium at high temperature may degrade the mold surface and, subsequently, the quality of the molded glass. Furthermore, pitting in the glass may be caused by particulate contaminants, such as contaminants from the mold. Pitting may also be caused by glass sticking to the mold surface where the glass to mold bond strength exceeds the strength of glass, creating divots in the glass due to so called “pullouts”. Other cosmetic defects such as stains and/or scuffing may be observed on 3D molded glass surfaces, especially when using high forming temperatures and longer contact times.
Accordingly, a need exists for molds with coatings that are compatible with high temperatures when shaping glass-based material.